Thermostatic switch



March 12, 1957 G. o. CHAPMAN 2,785,250

THERMOSTATIC SWITCH Filed Sept. 8, 1954 2 SheetsSheet l INVENTOR GALEN O. C HAPMAN HIS ATTORNEYS March 12, 1957 G. o. CHAPMAN THERMOSTATIC SWITCH 2 Sheds-Sheet 2 Filed Sept. 8, 1954 INVENTOR ALEN O. CHAPMAN @z HIS ATTORNEYS United States Patent THERMOSTATIC SWITCH Galen 0. Chapman, Boulder Creek, Calif. Application September 8, 1954, Serial No. 454,732 14 Claims. (Cl. 200-137) The present invention relates to a thermostatic switch, and pertains more particularly to a thermostatic switch having a housing of material with a high rate of thermal expansion, and a pair of contact struts of material with a lower rate of thermal expansion mounted within the housing.

The invention contemplates the provision of an improved and simplified thermostatic switch mechanism.

The invention also provides an improved tubular mounting structure with a sealed switch mechanism mounted within a portion thereof.

Another object of the invention is to provide an improved contact strut arrangement for a tube mounted thermostatic switch.

Another object is to provide a thermostatic switch having a pair of contact arms mounted respectively on a pair of support struts having portions disposed for differential movement in response to predetermined temperature changes to cause a relative wiping action by contacting portions of the contact members.

Another object is to provide improved switch mounting and temperature adjustment facilities for a tube type thermostatic switch.

Another object is to provide a thermostatic switch with contact support arms capable of substantial overstressing without danger of breaking or becoming permanently distorted.

Another object is to mount a pair of contact portions of a thermostatic switch within a pair of contact actuating struts to prevent the contact portions from short circuiting contact with an enclosing housing under extremes of temperature variation.

These and other objects and advantages of the invention will be apparent in the following description and the accompanying drawings, wherein Fig. 1 is a plan view of a switch assembly embodying the present invention as it appears when mounted on a supporting base plate.

Fig. 2 is a longitudinal sectional view through a portion of the switch structure during a temperature adjusting operation thereon, and before forming the end extensions of the housing. n

Fig. 3 is a view in side elevation of the switch structure shown in Fig. 1, portions thereof being broken away.

Fig. 4 is an enlarged transverse sectional view taken along line 44 of Fig. 5. m

Fig. 5 is an enlarged longitudinal sectional view of the switch portion of the device shown in Figs. 1 and 3 with the contact points mounted therein in open condition. Fig. 6 is a side elevation of the device shown in Fig. 5, a portion of the shell being broken away to show the switch elementsmounted therein, the contact points being shown in closed position.

Fig. 7 is a longitudinal sectional view generally similar to Fig. 5 but showing a modified form of mounting arrangement whereby the contact points separate on an increase of tem erature and closeon a decrease often:-

2 perature, the contact points being shown in closed condition.

Fig. 8 is a view similar to Fig. 7, the contact points being shown in open condition.

Fig. 9 is an enlarged transverse sectional view taken along line 9-9 of Fig. 7.

A thermostatic switch A embodying my invention (Figs. 1 and 2) comprises a tubular housing or shell 10 which may be thin walled tubing of metal having good corrosion resistance and a relatively high rate of thermal expansion. Thin wall brass tubing with an alloy ratio of 70% copper and 30% zinc is satisfactory in most instances.

The housing 10 preferably is heat treated before final forming to increase malleability and reduce grain size, so as to reduce the possibility of crystallization and fatigue of the housing metal by expansion and contraction thereof caused by temperature changes during the life of the device.

In making the housing 10, a work piece 11 of the desired tubing is provided of sufficient length so that extending end portions 12 and 13 of the tubing may be partially flattened and bent to extend laterally, in the same direction, from the central body portion 1.4 to form support legs 12a and 13a as shown in Fig. 2. Prior to flattening and bending the end portions of the tubing to form the legs 12a and 13a, an internal switch structure 17 (Fig. 3) is inserted and secured in position within the tubing 11. The switch structure 17 comprises, among other parts to be described later herein, a pair of contact support struts 18 and 19 having a pair of end plugs 20 and 21 of suitable material molded thereon. The plugs 20 and 21 preferably are molded of material having high strength and good dielectric properties such as phenol formaldehyde substance or suitable plastic material. Since many such materials are well known to those versed in the art of plastics molding, it will be unneces sary to enumerate them herein.

Conductor wires 22 and 23 are connected to the struts 18 and 19 respectively, and are carried through the tubing end portions 12 and 13 respectively. The free ends of the housing legs 12a and 13a (Fig. 2) preferably are flared somewhat at 25 and are molded into a base 27 of suitable dielectric material. The portions of the conductor wires 22 and 23 which extend beyond the legs 12a and 13a are embedded in, and are sealed to the material of the base 27 and are connected to conventional electric terminals 28 also molded into the base.

The two contact support struts 18 and 19 of the form of the invention shown in Figs. 3, 5 and 6 are in general similar to each other, and are mounted in relatively reversed position in the two plugs 20 and 21. Since the struts 18 and 19 are similar to each other, only the upper one 18 will be described in detail.

The strut 18 is of a suitable electrically conductive material preferably having a low coefiieient of expansion, relative to that of the housing 10, for example a nickelsteel alloy known as lnvar metal consisting of 36% nickel. The strut 18 has a straight end portion 30 which is secured, as by a crimped tongue 31 formed integrally therewith, to the conductor wire 22, which, as mentioned previously herein, extends outwardly through the flattened leg portion 12a of the housing. This tongue 31, being molded into the material of the plug 20, resists thrust stresses tending to displace the strut in the plug. The strut 18 is bent at 32 to provide an angularly offset portion 33 and is bent again at 34 to provide a portion 35 extending lengthwise of the tubing 11. The other end of this latter straight portion 3.5 is embedded in the other plug 21, and its extreme end vportion37 is bent at substantially right angles to the portion 35 10 have thrust interlocking engagement with the plug 21 into metal has afstraight portion 41 thereof aiiixed, as by welding or brazing, to the angularly ofiset strut portion 33 to'have electrical contact therewith. The contact support arm 40 is bent at 42 to have an arm portion 43 thereof extend generally, lengthwise of the straight strut portion 35. A usual type of contact point 44-is mounted on the free end of the contact support arm 43 as shown in Figs. 4 and 5 to face downwardly.

Thus, upon a contraction of the length of the housing relative to the strut it; caused by a reduction in temperature, the plugs and 21 are forced toward each other, and the straight, lengthwise extending strut portions 3% and exert opposite thrust forces on the two ends of the angularly offset portion 33 to which they are respectively connected. This action tends to swing the angularly disposed portion 33 in a counter-clockwise direction when viewed as in Figs. 5 and 6, and in so doing to swing the free end of the contact support arm 43 upwardly toward the position thereof illustrated in Fig. 5.

When the strut 18 is placed under tensile stress by an axial separation of the plugs 2t? and 21, upon a contraction of the length of the housing 10 relative to the strut 18 caused by a reduction in temperature, the angularly disposed strut portion 33 will be swung in the opposite or clockwise direction to swing the free end of the contact support arm 43 mounted thereon downwardly toward the position thereof shown in Fig. 6.

The lower strut 19 (Figs. 3, 5 and 6) is similar to the upper strut l3 and is mounted with its ends embedded in the plugs 29 and 21 in relatively reversed position from the strut 18. A lower contact support arm 47, similar to the upper contact support arm at), is mounted in a similar manner on the angularly offset portion 48 of the lower strut 19 and has a contact point 49 mounted on its free end facing the contact point 44 on the upper contact support arm 45. ing arrangement of the lower strut 19, it will be obvious from Figs. 5 and 6 that when the struts 18 and 19 are placed under tension the angularly offset strut portions 33 and 48 will tend to swing in opposite directions to separate the contact points 44 and 49, as shown in Fig. 5, while an endwise compressive force exerted on the struts will tend to move the contacts toward their closed position shown in Fig. 6. Also, when the angularly offset portions 33 of the two struts 13 and 19 thus are swung in opposite directions with the contact points 44 and 49 in contact with each other, a wiping action of the two points will be caused which tends to insure proper electrical contact of the points.

it will be noted, for example, in Fig. 5, that the struts 18 and 19 are positioned in the outward path of move ment of the contact support arms 43 and 47 so that no overstressing of the struts 13 and 19 could ever move either of these arms or the contact points 44 or 49 thereon into shorting contact with the housing it). This eliminates the necessity of providing an insulating sleeve or liner which otherwise might be secured within the hous ing it).

The plugs 20 and 21 have brass rings 50 and 51, respectively, molded one in each thereof. Each of these rings has a peripheral groove 52 therein which preferably is filed with a sealing substance 53, of a type which remains plastic and tacky for a substantial length of time, such as, for example, a silicone cement.

' Annular grooves 54 and 55 also are provided one in each of the plugs 20 and 21 at predetermined distances from the outer ends of the respective plugs, so that when the plugs 26 and 21 are mounted in properlyadjusted position in the housing 10, the wall material of the housing maybe indented into the grooves 52, 54 and 55 by conventional rolling or squeezing tools, not shown, to

Due to the relatively reversed mount- 5 anchor the plugs .firmly against axial displacement in the housing 19, and to seal the plugs to the housing.

In making the thermostatic switch A (Figs. 1 and 2) the entire internal switch assembly 17, including the conductor wires 22 and 23, is first completely assembled and is inserted in the undefoirned length of tubing 11 as shown in Fig. 3. The plug 2% then is secured in axially adjusted position in the tube 11 by deforming the wall metal of the tube into the grooves 52 and 53 of the ring 5t) and plug 20.

An adjusting screw 57 then is screwed part way into an internally threaded socket 58 fixedly molded in the other plug 21, and this screw is retained against axial displacement by suitable fixture means, not shown. In adjusting the switch as shown in Fig. 3, the conductors and 23 are connected to a test circuit 60 which may consist of an electric light bulb 61 and an electric battery 62 so that when the contact points 44 and 49 are closed the light bulb 61 will be illuminated.

With all of the parts shown in Fig. 3 at a predetermined temperature, and the tube 11 held against axial displacement relative to the screw 57 by suitable fixture means, not shown, the screw 57 is turned to adjust the second plug 21 axially of the tube 11 until the contact points 44 and 49 just barely make or break, as required, and as indicated by the test circuit 60. Thereupon the second plug 21 is secured in such axially adjusted position in the tube 11 by deforming the wall metal of the tube into the grooves 55 and 52 of the plug 21 and the brass ring 51, respectively.

In the modified contact arm mounting arrangement shown in Figs. 7, 8 and 9, most of the switch and housing components may be similar to those shown in Figs. 3 to 6 inclusive, and described previously herein. Such similar parts are designated herein by the same reference numerals as those applied to the corresponding parts in Figs. 5 and 6 with the prime added.

Contact support arms 64 and 75 (Figs. 7, 8 and 9) are bent at 66 to have attaching portions 67 and 68 respectively of each thereof directed oppositely from the attaching portion 41 of the contact arm 46 (Fig. 5). The angle of the bend 66 is such as to cause arm portions 69 and 70 (Figs. 7 and 8) to extend substantially parallel to each other into overlapping condition. Contact points 71 and 72 are mounted to face each other on the free ends of the contact support arms 64 and 75.

As will be obvious from the accompanying drawings in the light of the present description, the operation of the switch shown in Figs. 7, 8 and 9 is opposite to that shown in Figs. 3, 5 and 6, tending to open upon an elongation of the housing body portion 14' relative to the struts 18' and 19 caused by a rise in temperature, and to close upon a contraction of the housing relative to the struts caused by a drop in temperature.

Adjustment of the switch shown in Figs. 7, 8 and 9 is accomplishedin the same manner as that described previously herein for the arrangement illustrated in Fig. 3.

While the formation of the housing 10 and its mounting arrangement on a base 27 as shown in Figs. 1 and 2 is a feature of the present invention, the novel structure and mounting arrangement for the struts 18 and 19 and the contact arm assembly thereon also is an important improvement in switches of this character.

While I have illustrated and described a preferred embodiment of the present invention, it will be understood however, that various changes and modifications may be made in the details thereof without departing from the spirit and scope of the invention as set forth in the appended claims.

Having thus described the invention, what I claim as new and desire to protect by Letters Patent is defined in the following claims.

' Iclaim:

1. A thermostatic switch comprising a thermally expansible tubular housing, a head of insulative material secured in sealed adjusted relation to the housing at each end thereof, a pair of electrically conductive struts of low thermal expansibility relative to the housing mounted in thrust transmitting relation to said heads, both struts extending from head to head lengthwise within said housing in laterally spaced relation to each other and to the housing, an angularly oifset portion formed in each strut intermediately of said heads for angular displacement upon the transmission of thrust stresses to the struts by the heads, a contact support arm secured to the angularly offset portion of each strut for swinging movement upon an angular displacement of the offset portion, a contact point mounted on the free end of each support arm opposite the contact point on the other support arm, and conductor means connecting each strut through one of said heads to a point exteriorly of the housing.

2. A thermostatic switch comprising an expansible tubular housing, a head of insulative material secured in sealed adjusted relation to the housing at each end thereof, a pair of similar electrically conductive struts of low thermal expansibility relative to the housing mounted in relatively reversed condition to each other and in thrust transmitting relation to said heads, said struts extending lengthwise within said housing in laterally spaced relation to each other and to the housing, an angularly offset portion formed in each strut intermediately of said heads for angular displacement upon the transmission of thrust stresses to the struts by the heads, a contact support arm secured to the angularly offset portion of each strut for swinging movement beyond an angular displacement of the olfset portion, a contact point mounted on the free end of each support arm opposite the contact point on the other support arm, and conductor means connecting each strut through one of said heads to a point exteriorly of the housing.

3. A thermostatic switch comprising a thermally expansible tubular housing, a pair of supports secured in axially spaced relation within the housing, a pair of struts of low thermal expansibility relative to the housing mounted on said supports and extending lengthwise therebetween in laterally spaced relation to each other and to the housing, an angularly ofi'set portion formed in each strut intermediately of said heads, a contact support arm secured to the angularly offset portion of each strut and extending lengthwise of the housing into overlapping relation with the other support arm, a contact member mounted on the free end of each support arm opposite the contact member on the other support arm for movement into and out of contact with each other upon predetermined temperature changes of the housing and struts, and an electrically conductive path from each contact member to a point exteriorly of the housing.

4. A thermostatic switch comprising a thermally expansible tubular housing, a pair of insulative support plugs sealed in axially adjusted spaced relation within the housing, a pair of metal strip struts of low thermal expansibility relative to the housing anchored to said plugs and extending lengthwise therebetween in laterally spaced relation to each other and to the housing, an angularly offset formed in each strut in longitudinally spaced relation to the similarly oifset portion of the other strut, a contact support arm secured to the angularly oifset portion of each strut and extending lengthwise of the housing toward the angularly offset portion of the other strut, a contact member mounted on the free end of each support arm and located for movement into and out of contact with the other contact member upon predetermined temperature changes of the housing and struts, and an electrically conductive path from each contact member through one of said plugs to a point exteriorly of the housing.

5. In a thermostatic switch having an expansible tubular housing with a pair of sealing plugs mounted in axially spaced relation therein, a strut of low thermal expansibility relative to the housing secured to the two plugs and extending lengthwise therebetween, an angularly offset portion formed in said strut immediately of the two plugs, a contact support arm secured to the oliset portion of the strut and extending lengthwise of the housing, a contact element carried on the free end of the support arm, a second contact element mounted in the housing in a position for malte-and-break relation with the contact element on the support arm upon predetermined expansion and contraction of the housing relative to the strut, thereby exerting tensile and compressive stresses on the strut and causing angular movement of the angularly ofiset portion thereof to swing the support arm mounted on the offset portion, and an electrically conductive path from each contact element to a point exteriorly of the housing for connection of the switch to an electrical circuit.

6. in a thermostatic switch having an expansible tubular housing with a pair of sealing plugs of electrically insulative material mounted in axially adjusted, spaced relation therein, a pair of similar, reversely mounted struts of low thermal expansibility relative to the housing secured to the two plugs to extend lengthwise therebetween within the housing and in spaced relation to each other and to the housing the end portions of said struts extending lengthwise of the housing, an angularly ofiset portion formed in each strut intermediately of its end portions, a pair of similar contact support arms secured one to the oltset portion of each strut, and extending lengthwise of the housing, a contact element mounted on the free end of each support arm, and located for movement into and out of contact with each other, upon predetermined expansion and contraction of the housing relative to the struts whereby the struts are subjected to tensile and axially compressive stresses swinging the angularly ofiset portions and the contact support arms thereon, and means electrically connecting each contact element to a point outside the housing for connection of the switch to an electrical circuit.

7. A thermostatic switch comprising a thermally expansible body, a pair of insulative strut supports mounted in adjusted, spaced apart relation on said body, a pair of struts having dilrerent rates of thermal expansion than said body anchored at both ends of each thereof to said supports, one of said struts having an auguiarly portion therein for swinging movement upon rel"ti expansion between the body and the struts, a i. support arm secured at one end thereof to the offset portion of said one strut and extending lengthwise of the housing for swinging movement therewith, a first contact element on the other end of said support arm, a second coat ment carried by the oth r strut and positions said first contact element for contact first contact element upon pretic sive movements of body an strut with the angularly oiset r to lengthwise stresses swingi a tr and the contact support arm se ther for electrically connecting said contact elements into an electric circuit.

mounted in adjusted, spaced apart remr-on on a member, a strut of a material has i thermal expansion than said ing between and anchored at both ends insulative supports, strut having portion therein disposed at an a line joining the anchorages of contact support arm secured at one on angularly offset portion of said strut, hr" ment on-the free end of said support arm, element carried by the body member and if:

,c ted said first contact element or contact and first contact element upon predetermined re e expansive movements of the body member, and the strut, whereby the strut is subjected to axial stresses thereby causing a relative swinging movement of the angularly ofiset portion and the support arm thereon and means for'electrically connecting each contact element into an electric circuit.

9. In a thermostatic switch having a thermally expansible body member and a pair of insulative strut supports mounted in adjusted, spaced apart relation on said body member, a strut of a material having a different rate of thermal expansion than said body member anchored at both ends thereof to said supports, said strut having an angularly offset portion therein for swinging movement on an extension or contraction of the strut, a contact support arm secured at one end thereof to said angularly offset portion for swinging movement therewith, a first contact element on the free end of said support arm, and a second contact element mounted opposite said first contact element for selective contact and release by said first contact element upon predetermined relative expansive movements between the body member and the strut.

10. For mounting in the thermally expansible tubular housing of a thermostatic switch; a strut formed of a strip of metal having a rate of thermal expansion different from that of the housing, said strut consisting of two generally parallel end portions, and an intermediate portion joining the inner ends of said end portions and offset at an acute angle thereto, whereby the application of opposed endwise forces to the two end strut portions tends to swing the intermediate strut portion, a contact support arm secured to the angularly offset strut portion for swinging movement therewith, and a contact point mounted on the free end of the support arm.

ll. For mounting in the thermally expansible tubular housing of a thermostatic switch; an internal switch assembly comprising a pair of insulative plugs of a size to fit slidably within the housing, a pair of similar struts anchored at opposite ends thereof to said plugs, each strut being formed of a strip of metal having a rate of thermal expansion different from that of the housing, each strut consisting of two generally parallel end portions, and an intermediate strut portion joining the inner ends of said strut end portions and oflset at an acute angle thereto, whereby the application of opposed endwise forces to the two end portions of each strut tends to swing the intermediate strut portion, a contact support arm secured to each angularly ottset strut portion for swinging movement therewith, and a contact point mounted on the free end of each support arm, said struts being mounted in said plugs in relatively reversed condition with the contact points located opposite each other for moving into and out of contact with each other upon the application of predetermined opposed endwise forces to said plugs and thence to the end portions of said struts attached thereto.

12. A thermostatic switch structure comprising a tubular housing having a straight central portion and an angularly ofiset partially flattened tubular supporting leg portion on each end thereof and coextensive therewith, a pair of electrically insulative support plugs secured in axially spaced adjusted relation within thecentral housing portion, a pair of electrically conductive struts having a different rate of thermal expansion from the housing secured to extend lengthwisebetween said insulative support plugs,

contact points carried by said struts for movement into and out of contacting relation with each other upon predetermined relative expansion and contraction between the central housing portion and the struts, an electrically insulative base enclosing the terminal ends of the leg portions of said housing and in sealing relation therewith, a pair of conductors connected one to each of said struts and extending in insulated relation through one of the legs of said housing and into said base, and a terminal member on said base electrically connected to each conductor.

13. A thermostatic switch structure comprising a tubu lar housing having a straight central portion and an angularly ofiset partially flattened tubular supporting leg portion on each end thereof and coextensive therewith, a pair of electrically insulative support plugs secured in axially spaced adjusted relation within the central housing portion, a pair of struts having a'difierent rate of thermal expansion from the housing secured to extend lengthwise between said insulative support plugs, contact points carried by said struts for movement into and out of contacting relation with each other upon predetermined relative expansion and contraction between the .central housing portion and the struts, an electrically insupport plugs and one of the legsof said housing and into said base, and a terminal member on said base electrically connected to each conductor.

14. A thermostatic switch of the character set forth comprising a thermally extensible sealed housing, a pair of struts of metal strip stock having a diiferent rate of thermal expansion from the housing secured to the ends of said housing to extend therebetween, an angularly oifset portion in each strut intermediate its ends for angular displacement by a relative expansive movement between the housing and struts, a contact support arm having its base secured to the angularly offset portion of one strut and its free end extending toward the angularly offset portion of the other strut, and a contact member mounted on the outer end of each support arm opposite to and facing the contact member of the other'ar'rn.

References Cited in the file of this patent UNITED STATES PATENTS 1,942,002 Romanelli Jan. 2, 1934 2,307,867 Smith Jan. 12, 1943 2,317,828 7 Turenne Apr. 17, 1943 

